Recently, a scanner system has been widely used in the manufacture of printing plates. For forming images using the scanner system, various recording apparatus are employed. Recording light sources for these scanner system recording apparatus include a glow lamp, a xenon lamp, a tungsten lamp, a light emitting diode (LED), a He-Ne laser, an argon laser, a semiconductor laser, etc.
Newly developed scanner systems employ a dot generator based system of directly, by electrical means, forming dots or characters. As the scanner light source for the dot generator system, a high output argon laser had hitherto been used. However, since the above light source is bulky and expensive, dot generator system recording apparatus using a He-Ne laser light source (632.8 nm) or an LED light source (660 to 650 nm), which are more compact and inexpensive, have recently been developed. The light-sensitive materials for use in the scanner apparatus require certain characteristics. In particular, the light-sensitive material must have a high spectral sensitivity for each wavelength of the scanner light source and must also have a high sensitivity and a high contrast even when exposed with a high illuminance source and for a short exposure time of from 10.sup.-3 to 10.sup.-7 seconds. The above conditions are typically employed in a scanner recording apparatus. Furthermore, in the field of facsimile, the light-sensitive material must be able to endure high-temperature fast processing for quick reporting and must also be able to be handled in a bright green safelight in order to allow for efficient operation. With the increase in scanning speed, the increase of line density for improving the image quality, and the sharpening of the scanning light beam, the development of a light-sensitive material having a higher sensitivity and a higher contrast has been strongly desired.
In order for the light-sensitive material to have a high sensitivity and a high contrast under conditions of high illuminace and short exposure times of from 10.sup.-3 to 10.sup.-7 seconds using an LED light source or a He-Ne laser light source, the sensitivity of the silver halide emulsion or the spectral sensitivity of a silver halide emulsion thus sensitized must be high at the above conditions. A method frequently used for this purpose involves increasing the sensitivity of the silver halide emulsion by introducing an iridium salt into the silver halide as described in JP-A-48-60918, JP-A-58-211753, JP-A-61-29837, and JP-A-61 201233 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") and JP B-48-42172 (the term "JP-B" as used herein means an "examined Japanese patent publication"). Also, spectral sensitizing dyes for generally obtaining red-sensitive silver halide emulsions are described in JP-B-48-42172 and JP-B-55-39818 and JP-A-50-62425 and JP-A-54-18726.
Preferred silver halide emulsions for red-sensitive emulsions comprise mono-dispersed gold- and sulfur-sensitized silver iodobromide emulsions having a cubic or tetradecahedral crystal habit as described in JP-B-52-21366 and Japanese Patent Application Nos. 63-16256 and 63-64119.
Such high-sensitive emulsions may have a high sensitivity and a high contrast to practical light exposure but, on the other hand, have a reduced pressure resistance and, in particular, fog due to pressure is liable to occur.
Also, silver halide grains having a core/shell structure have hitherto been developed for increasing the sensitivity and improving the image quality by employing the development inibiting effect of iodide ions. These techniques are described in JP-A-59 188639, JP-A-59 177535, JP-A 59-181337, JP-A-59-192241, JP-A-60-11838, JP-A-60-138538, and JP-A-60-254032. Silver halide emulsions having a core/shell structure may be advantageous with respect to high sensitivity and pressure resistance, and in particular, fog due to pressure is reduced as compared with a silver halide emulsion having uniform structure grains, but the performance thereof has not yet been satisfactory.
Pressure is applied to light-sensitive materials in the manufacture thereof and when transporting and cutting the material. Also, pressure is unavoidably applied to the light-sensitive material in light exposure and development thereof.
When pressure is applied to a light-sensitive material, the pressure is applied to the silver halide grains through gelatin or other high molecular binder material. When pressure is applied to silver halide grains, blackening or desensitization can occur regardless of the exposure amount as reported, e.g., in K. B. Mather, Journal of Optical Society of America, 38, 1054 (1948) and P. Faelens, Journal of Photographic Science, 2, 105 (1954).
As a means for avoiding the change of density by the applied pressure, a method is known of cushioning the pressure before reaching silver halide grains by incorporating a polymer or a plasticizer in the silver halide emulsion, or by reducing the ratio of silver halide/gelatin in a particular silver halide emulsion layer or in the light-sensitive material.
In this regard, British Patent No. 738,618 discloses a method using a heterocyclic compound, British Patent No. 738,637 discloses a method using an alkyl phthalate, British Patent No. 738,639 discloses a method using an alkyl ester, U.S. Pat. No. 2,960,404 discloses a method using a polyhydric alcohol, U.S. Pat. No. 3,121,060 discloses a method using a carboxyalkyl cellulose, JP-A-49-5017 discloses a method using paraffin and a carboxylate, and JP-B-53-28086 discloses a method using an alkyl acrylate and an organic acid.
According to those methods using a plasticizer, however, the amount of plasticizer is limited so as not to reduce mechanical strength of the emulsion layer. On the other hand, when the ratio of silver halide/gelatin is increased, the resulting light-sensitive material has a low developing speed and loses the property for quick processing.
A polymer having an acid group is introduced into silver halide emulsion layers for various purposes and these techniques are disclosed, for example, in U.S. Pat. Nos. 3,062,674 and 3,287,289 and JP-A-61-228437, JP-A-62-55642, JP-A-62-220947, JP-A-62-222242, and JP-A-62-247351.